Technical Field
The present invention relates to a vinyl polymer powder, a curable resin composition comprising the vinyl polymer powder and a cured substance of the curable resin composition.
Background Art
Resin materials used in fields of electronics are considered as important with improvement of technologies of IT such as mobile devices, digital appliances, communication devices, and electronic devices for vehicles.
For example, there is rapidly increased demand for thermosetting resins or active energy-ray curable resins, such as epoxy resins, polyimide resins, curable acrylic resins, and curable oxetanic resins, superior in heat resistance or insulating properties.
In particular, resin compositions comprising epoxy resins have high glass transition temperature and are excellent in insulating properties, flame retardant properties, and adhesiveness, so that resin compositions comprising epoxy resins are used for various fields such as sealing materials of semiconductors, insulating materials, and adhesives.
Above all, fluidal epoxy resins at room temperature are used for various paste type or film type materials because of applicability of use for casting or coating.
Specifically, they are used for various applications such as fluidal sealants like primary-mounting under-filling materials, secondary-mounting under-filling materials and glob-top materials in wire bonding; sealing sheets to seal various tips on boards in the lump; pre-dispensing type under-filling materials; sealing sheets to collectively seal on a wafer level; adhesion layers for three layer-copper-clad laminates; adhesion layers for die bond films, diagram touch films, layer-insulation films, cover-lay film, and the like; adherent pastes such as die bond pastes, layer-insulation pastes, conductive pastes and anisotropic conductive pastes; sealants for light emitting diodes; optical adhesives; and sealing materials of various flat panel displays like a crystalline liquid and an organic electroluminescence.
In recent years, it becomes important that the above epoxy resin compositions can be applied for fine processing such as precise injection or coating by a dispenser, precise pattern-coating by screen-printing, and coating on films with high film thickness-precision.
For the above applications, it is important that these epoxy resin compositions are stable for viscosity characteristics and conspicuous lowering or rising of the viscosity by environmental temperature is fatal.
However, viscosities conspicuously decrease by rising of temperature before curing because epoxy resin compositions have much time for hardening and much dependency of viscosity on temperature, so that highly precise coating or pattern formation is difficult.
For example, it is necessary having high flowability of epoxy resin compositions to pour epoxy resin compositions into slits having dozens of micrometers using dispensers, when epoxy resin compositions are used as under-filling materials.
However, when flowability of epoxy resin compositions are high, viscosity at heating of epoxy resin compositions are lowered before curing and epoxy resin compositions begin to flow, so that a damage such as contamination of board or circuit, near the pouring portion, or restraint of basic sealing performance is generated.
In addition, when epoxy resin compositions are used as adhesives for films such as copper-clad laminates and die bonding films, it may occur a problem that film thickness of the adhesives fluctuates because epoxy resin compositions flow out by severe lowering of viscosities of epoxy resin compositions, in the case of heat hardening of coating with arranging to constant film thickness at room temperature.
Thus, in fields of especially electronic materials, there is an extremely strong demand that a viscosity of epoxy resin composition to be used should not deteriorate when a temperature of the epoxy resin composition is raised and that a form should be early stabilized, by a request for highly precise processing rising year by year.
Method to give such the characteristics to an epoxy resin composition includes a method to blend a rubbery particle suitable for an agent for imparting gelation characteristics (hereinafter referred to as “a pre-gel agent”) to immediately obtain a gel state of an epoxy resin composition by heating.
However, the rubbery particle is insufficient for ability to give gelation characteristics and fusion between particles is strong because of lowness of glass transition temperature, so that it is difficult to disperse in primary particles in a liquid material such as an epoxy resin.
In addition, there is not especially considered ion purity (ion concentration) of rubbery particles.
As a demand for epoxy resin compositions in fields of recent electronic materials, not only obtaining of simple gelation characteristics but also high ion purity (namely, low ion concentration) to reduce influence to electrical characteristics, high permeability with immediate permeation into a narrow pitch, and extremely short-time gelation speed are required at the same time.
Up to the present, materials satisfying these requirements were not proposed.
For example, in patent document 1, a method to use a vinyl polymer particle as a pre-gel agent is proposed.
In this approach, gelation characteristics can be given to an epoxy resin composition.
However, there cannot be obtained satisfaction for support to tendency for finer pitch or thinner thickness, required in fields of electronic materials because dispersibility to primary particles of the vinyl polymer particle is not sufficient.
In addition, a granular structure is generated to give an inferior quality when the epoxy resin composition is thinly coated on a base film.
Also, there is not considered ion concentration of the epoxy resin composition.
In patent document 2, a method to use an ion cross-linked rubbery particle as a pre-gel agent is proposed.
In this approach, ions are inevitably contaminated in a cured substance obtained because gelation characteristics is given by ionic cross linking, so that this method is unsuitable for fields of electronic materials.
Of course, gelation characteristics cannot be given because ionic cross-linking may not be obtained when ion concentration of an epoxy resin composition is intended lowered.